Today, GNSS and EDM are well-known technologies for survey positioning. Precision positioning with GNSS (e.g., the well-known Global Positioning System (GPS) operated in the United States) is commercially available using high-precision GNSS receivers capable of centimeter accuracy in geodetic and surveying applications.
However, the use of such high-precision GNSS receivers can be adversely impacted depending upon certain physical or line of sight factors. That is, the accuracy of such receivers diminishes when the lines-of-sight associated with one or more satellite signals pass through large structures (e.g., buildings), dense foliage, or other objects that effectively block or degrade the GNSS signals transmitted from the satellites. As such, deployment of high-precision GNSS in applications that may involve significant GNSS signal blocking and/or signal degradation can be challenging.
Of course, there are other existing location and surveying technologies that are not as severely impacted by such line of sight factors as noted above with respect to GNSS. An EDM is one established, commercially available device that is typically laser-based and the accuracy of which is derived from an internal reference frequency source (e.g., a crystal oscillator) that is subject to precise calibration. For example, using a well-known “intersection” surveying technique (hereinafter the “Intersection Method”), a user can select three (3) points that are GNSS-accessible and do not lie on a straight line and measure their coordinates with a GNSS receiver and, from the same points, measure the distance to the remote target point using an EDM and compute the three dimensional (3D) coordinates of the remote target point. One potential drawback of such an EDM technique is that it allows for the measurement of only one point at a time.
Another well-known technology that avoids line-of-sight effects is close range photogrammetry. Photogrammetry is a technique of making measurements from photographs and is used in surveying applications for determining terrestrial or 3D space position of points, and the distance and angles between them. Typically, these points are associated with positions of the surface of the Earth, and are used for a variety of land-based and aerial surveying applications. For example, a user might take two (2) photographs of certain target point(s), with a specially calibrated camera, from the same two (or more) locations as measured with a GNSS receiver, and then process the photographs using well-known photogrammetric software to determine the precise orientations of the cameras when the image were taken. Advantageously, the coordinates of all visible points can be measured from a single set of images. On the other hand, photogrammetry can be a time consuming process and requires a high degree of computational power that may limit its use with handheld devices in the field of operation. Also, the accuracy of this technique is severely impacted by certain highly reflective surfaces, and is heavily dependent upon the quality of the images used which may be adversely impacted by light conditions, image angles, and surface types, to name just a few.
Therefore, despite the advances in and availability of a variety of a surveying techniques and associated equipment, a need exists for an improved technique for increasing high-precision surveying accuracy, and in particular, with respect to remote multi-point applications in areas where the transmission of GNSS signals are blocked and/or degraded.